In the handling of particulate material, it is sometimes required to accurately and continuously monitor the mass flow rate of the material. Such a need arises, for instance, when a treatment chemical is to be dosed onto the particulate material at a predetermined rate of a chemical per unit mass of the particulate material. Ideally, under these circumstances, the mass flow rate should be maintained as constant as possible, so that the dosage rate of treatment chemical may also be maintained at a constant rate. However, in practice, the mass flow rate of particulates tends to vary so that the dosage rate per unit mass also varies. This variation in dosage is particularly troublesome in those cases where the level of treatment chemical is specified by regulation. Clearly, variation of mass flow rate, while maintaining a constant dosage rate, increases the risk of overdosing portions of the flowing particulate material, and underdosing other portions as the mass flow rate varies.
In order to maintain uniform dosage of a treatment chemical onto a flowing mass of particulates, it is desirable to have a means for measuring the instantaneous mass flow rate accurately and precisely. Moreover, it is desirable to use this information to virtually instantaneously, and continuously, control a treatment chemical dosage pump so that the dosage rate is automatically adjusted to compensate for changes in the mass flow rate of particulates. Preferably, the apparatus for measuring the mass flow rate of the particulates should be robust, inexpensive, require little maintenance, and able to measure flow rates over the complete range of mass flow rates that are expected to be encountered.
It also is often necessary to accurately measure the total mass of particulate material. It can be extremely cumbersome to perform such measurement by the typical method of placing a quantity of the particulate matter in a receptacle for weighing on a scale. It would be much more convenient to simply measure the total mass of the particulate matter during a transfer process, for instance as a particulate matter is extracted from a storage unit. However, heretofore such flow measuring devices have not proven to be very accurate.